JP2007056875A - Oblique tip hole turbine blade - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an oblique tip hole turbine blade including improved tip cooling capacity. <P>SOLUTION: A turbine blade 10 includes a hollow blade profile part 12. The blade profile part extends with passing through a tip floor 28 and includes a plurality of curved tip holes 42 oblique toward a squealer rib 34 extending outward from the floor 28. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates generally to gas turbine engines, and more specifically to turbine rotor blades for gas turbine engines.

  In a gas turbine engine, air is pressurized in a compressor and mixed with fuel in a combustor to generate hot combustion gases. The high pressure turbine (HPT) extracts energy from the combustion gas and supplies power to the compressor, and the low pressure turbine (LPT) extracts energy from the combustion gas and supplies power to the upstream fan in aircraft turbofan engine applications. Alternatively, power is supplied to the output shaft for marine and industrial applications.

  The first stage turbine rotor blade initially receives the hot combustion gases from the combustor and is therefore exposed to that high temperature. Thus, the first stage turbine blade is formed of the finest superalloy that maintains strength in the harsh environment of HPT to maximize the useful life of the blade.

  In addition, each turbine blade is hollow and includes specially configured cooling circuits therein that use a portion of the air extracted from the compressor during operation to internally cool the turbine blades. At the same time, an external insulation air film is formed by spent air discharged from the turbine airfoil through the various film cooling hole rows.

  Each blade includes an airfoil extending outwardly from a platform joined to a dovetail for individually attaching the blade to the outer periphery of the support rotor disk. The airfoil has a generally concave pressure side and a generally convex suction side, the sides being radially extending over the length of the airfoil from the root of the airfoil at the platform to its radially outer tip. And extends axially across the chord between opposing leading and trailing edges.

  Many cooling circuits found in the airfoil are specially tuned to cool different parts of the airfoil differently for different heat loads from the combustion gas flowing on the opposing positive and negative pressure sides. It can have the structure of. The concave-convex configuration of the airfoil creates different speed and pressure distributions on its surface during operation to maximize energy extraction efficiency from the combustion gas for rotating the support disk.

  Thus, the heat load due to combustion gases varies in a complex three-dimensional pattern from the root to the tip and from the leading edge to the trailing edge, which in turn affects the local cooling requirements of different parts of the airfoil It will be.

  Each airfoil has a maximum thickness just behind the leading edge and gradually becomes thinner toward the thin trailing edge. In general, each airfoil also includes a small extension of the pressure and suction sides at the tip of the airfoil that extends from the tip floor that divides the top of the internal cooling circuit and opens an open tip cavity. Enclose squealer ribs.

  The leading edge of each airfoil that initially receives hot combustion gases, the thin trailing edge of each airfoil, and the small squealer ribs at the tip of the airfoil are configured differently, have different functions, and are not There are problems inherent in its construction to obtain sufficient cooling to ensure a long useful life of the blade.

  Modern turbine blades have been in development for decades, and their development allows their useful life to be multi-year free of undesirable thermal damage that would limit their useful life. Or a significant increase to thousands of hours of gas turbine engine operation. However, despite the majority of blades having unbreakable performance, the life of turbine blades is nevertheless limited by local thermal failure in either region.

  For example, a turbine blade tip is an area of a blade that is difficult to cool sufficiently over the desired long useful life of the blade. Skiler ribs surrounding the airfoil tip provide positive pressure to minimize the radial gap or gap between the tip and the surrounding turbine shroud and to minimize unwanted combustion gas leakage through the gap during operation. And as a local extension of the suction side. Since the turbine blades are subject to accidental friction with the surrounding turbine shroud, the small squealer rib ensures the integrity of the tip floor that partitions the internal cooling circuit while reducing the negative effects of tip friction.

  The squealer rib itself is a solid material and is relatively thin, immersed in a hot combustion gas that flows axially along the pressure and suction sides and radially on the pressure side during operation and is in operation. When the gas leaks beyond the tip, it is immersed in the hot combustion gas flowing through the tip gap with the surrounding turbine shroud. Thus, the squealer ribs are exposed to heating along their radially outermost edges with heating from both their outside and inside of the tip cavity. The tip also experiences a high centrifugal velocity of the airfoil tip during operation and a high velocity of hot combustion gas that flows downstream during operation.

  Therefore, there are many different configurations in the prior art for cooling turbine blade tips that have different complexity, different performance and different effectiveness in an engine that operates over its intended long useful life. Have.

  The turbine blade tip typically includes a plurality of tip holes that extend vertically through the tip floor and fill the tip cavity with spent cooling air from an internal cooling circuit. In this manner, spent cooling air improves tip cooling against the entry of hot combustion gases into the tip cavity.

  In addition, film cooling holes are typically found near the blade tip on the pressure side so as to form a film that cools the pressure side squealer ribs during operation. In both configurations, the used cooling air provides local film cooling of the outer and inner surfaces of the squealer ribs.

  Since used cooling air is discharged through the tip hole under pressure, the air is discharged in the form of a high-speed individual jet perpendicular to the tip floor, which limits its cooling effect. Therefore, a symmetrically widened tip hole that penetrates the tip floor is introduced to diffuse the discharge air to reduce its speed and correspondingly increase the pressure to increase the cooling inside the tip cavity. Can do.

  In yet another conventional tip cooling configuration, the cylindrical tip hole tilts the tip floor so that it specifically cools the inner or inner surface of the airfoil pressure side squealer rib having the greatest thermal load there. It can be penetrated. However, since the tip holes have a relatively small diameter, the tip holes cannot be formed in the original casting process of the blade itself, and must be formed by drilling after casting. Drilling requires access to the tip floor without damaging the cast squealer ribs. In order to do this effectively, the inclined tip hole must be placed close to the squealer rib, which interferes with the production of the proximal tip hole.

Thus, prior to the formation of the squealer ribs, the inclined tip holes must be made first, followed by the squealer ribs, which increases the difficulty and cost of manufacture and generally directional solidification. The single structure between the squealer rib and the main airfoil portion made of a superalloy or a single crystal alloy is damaged.
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  Accordingly, it would be desirable to provide a turbine rotor blade having improved tip cooling.

  The turbine blade includes a hollow airfoil that has a plurality of curved tip holes that extend through the tip floor and are angled toward a squealer rib extending outwardly from the floor.

  In the following detailed description, taken in conjunction with the accompanying drawings, the invention in accordance with preferred and exemplary embodiments will be more particularly described with further objects and advantages thereof.

  Illustrated in FIG. 1 is an exemplary HPT turbine rotor blade 10 for use in a gas turbine engine. The blade includes a hollow airfoil 12 that extends radially outward from a platform 14 that is integrally formed with the support dovetail 16. The dovetail is configured to support the blade in a corresponding slot in the perimeter of the turbine rotor disk 18 shown partially.

  The airfoil portion 12 includes a substantially concave pressure side wall 20 and a substantially convex suction side wall 22 that faces in the circumferential direction, and these side walls are spaced apart in the lateral direction (blade thickness direction). To form an internal cooling circuit or channel 24 between them. The airfoil also extends radially or longitudinally from the radially inner root 26 at the junction with the platform 14 to the radially outer flat tip floor 28 at the opposite distal tip of the airfoil. The two sidewalls also extend axially across the chord between opposing leading and trailing edges 30,32.

  Small squealer ribs 34 extend integrally from the side walls 20, 22 around the tip floor 28 as a unitary or integral casting with the airfoil. The squealer rib extends along the side walls between the leading edge and the trailing edge to form a tip cavity 36 on the floor that is open radially outwardly into the gas turbine engine. When installed, it faces the surrounding turbine shroud (not shown).

  In operation, a dovetail base having one or more inlets in which pressurized cooling air 38 is bled from an engine compressor (not shown) and coupled in flow communication with the internal cooling circuit 24 of the blade. Led through. The airfoil may have any conventional cooling circuit within it to expel used cooling air through various rows of film cooling holes and trailing edge holes of any conventional design and configuration.

  In this way, the cooling air is first used to internally cool the airfoil and then discharged through film cooling holes along both the positive and negative side walls of the airfoil to produce a combustor ( A corresponding thin film of cooling air is formed which insulates the hot combustion gas 40 discharged from (not shown).

  As described above in the Background section, the tip region of the blade 10 burns simultaneously with hot combustion gases along the outside of both the positive and negative pressure sidewalls during operation and with a small squealer rib 34 that bounds its periphery. It is particularly difficult to cool in view of direct exposure to hot combustion gases along the inside of the ribs as the gas flows or leaks over the squealer ribs.

  Accordingly, the turbine blade shown in FIG. 1 includes an improved configuration for tip cooling, in which a plurality of curved tip holes 42 are in flow communication with the cooling circuit 24 to receive cooling air from the cooling circuit 24. And extends through the tip floor 28.

  FIG. 2 shows a tip hole 42 according to an exemplary embodiment, in which the corresponding hole 42 directs the cooling air 38 at a shallow or oblique viewing angle with the squealer rib 34. As shown, it is slanted or curved toward the squealer ribs 34 on each side of the airfoil. The squealer ribs 34 are preferably cast integrally with the airfoil itself with a typical superalloy that has high strength at high temperatures, and the tip holes 42 are the ribs 34 where the ribs 34 join the floor. Proximate to the base and disposed through the floor 28. The hole is inclined outwardly toward the inner surface or the inner surface of the squealer rib 34 so that cooling air discharged from the hole is deflected or directed in the blade thickness direction toward the inner surface of the rib to enhance its cooling effect. Have

  As shown in FIG. 2, each of the tip holes 42 includes a linear inlet 44 that extends through the bottom surface of the floor 28 in flow communication with the cooling circuit 24 to receive air from the cooling circuit 24. Each hole 42 also includes an integral outlet 46 that is angled or curved from the inlet 44 toward the inner surface of the adjacent rib 34. The outlet 46 deflects or bends the air jet from the outlet 46 against the inner surface of the rib to form a diagonal impingement cooling form of the air jet and forms a thin film of cooling air from the air. Tilt outwardly or tilt toward the squealer ribs 34 to improve insulation.

  The tip hole 42 is shown in a cross-section in the lateral direction (blade thickness direction) in FIG. 2, and in FIG. 3 in a cross-section in the side direction (blade chord direction). The flow passage area is expanded or increased from the inlet 44 so that the cooling air 38 is diffused with a directivity toward the squealer rib 34 as opposed to inward toward the central portion of the tip cavity. is doing.

  The inlet 44 preferably has a finite length that is approximately half the thickness of the tip floor 28, is preferably axisymmetric along its central axis, and can be rectangular in shape as shown in FIG. Alternatively, it can be square, circular or oval as desired in performance and manufacturing system.

  Accordingly, the outlet 46 is asymmetric in the blade thickness direction toward the rib 34 as shown in FIG. 2, but is further symmetrical in the chord direction along the rib 34 as shown in FIG. preferable.

  In this way, the air jet discharged from each tip hole 42 is deflected so as to bend outward toward the inner surface of the squealer rib 34 as shown in FIG. 2, but as shown in FIG. It extends in both directions, the forward direction toward the leading edge in the chord direction and the backward direction toward the trailing edge. Accordingly, while maximizing the effective reach of the air discharged from each tip hole 42, the cooling air is further deflected or bent outwardly so as to graze the inner surface of the rib.

  In the embodiment shown in FIGS. 2 and 3, the inlet 44 is perpendicular or substantially perpendicular to the floor 28 when the floor 28 is substantially flat. Correspondingly, the curved outlet 46 includes a flat front wall 48, as shown in FIG. 2, which is located proximate to the base of the squealer rib 34 and out towards the rib 34. It is inclined at a shallow inclination angle A from the entrance 44. Each outlet also includes a flat rear wall 50 spaced inwardly from the front wall 48 and substantially in line with the rear surface of the inlet 44.

  A pair of flat side walls 52 are provided to connect the front and rear walls 48, 50 together at corresponding small arcuate joints between them to complete the quadrilateral configuration of each outlet 46 and surround the periphery of the outlet.

  The slanted tip holes 42 shown in FIG. 2 have a relatively small flow path area, so these tip holes are formed after the airfoil itself is originally cast with a solid casting tip floor 28 by another method. Preferably it is done. In this way, the squealer ribs 34 are originally cast as an extension of the positive and negative side walls 20, 22, and the squealer ribs 34 extend from both side walls and have the same metallurgical properties as the side walls, ie gas It has the characteristics of a special superalloy used to obtain high strength in high temperature operation in the severe environment of turbine engines.

  Individual tip holes 42 can then be fabricated by using correspondingly shaped electrical discharge machining (EDM) electrodes 54 having distal ends configured to match the desired shape of the oblique outlet holes 42. it can. As shown in FIG. 2, the distal end of the EDM electrode 54 is configured to perforate the hole inlet 44 and conform to the shape of the hole inlet 44 to form a forward wall to form a beveled outlet 46 in the tip hole. Inclination jogs that coincide with 48 inclination angles A are included.

  The electrode 54 can then be lowered vertically into the tip cavity 36 close to the squealer rib 34, and translating the electrode axially downward will drill the final tip hole 42 by the EDM process. .

  Since the outlet 46 is angled outwardly toward the rib 34, the corresponding electrode 54 has a corresponding jog that is inclined outwardly toward the same rib 34, the jog being the inner surface of the rib. Is supported by vertical shanks that are spaced apart by a suitable distance C. The interval C should be large enough to prevent pre-cast squealer ribs 34 from being subjected to stray electric discharge machining when the electrodes are lowered during the hole forming process.

  The tip hole inlet 44 formed by the EDM process can be relatively small, its effective diameter is about 10-15 mils (0.25-0.38 mm), and the blade thickness direction of the electrode shank The interval C is the same size in order to prevent stray electric discharge machining.

  Since the rear wall 50 is aligned perpendicular to the inlet 44 and both are substantially perpendicular to the flat tip floor 28, the EDM electrode 54 has an oblique tip hole 42 that includes its inclined front wall 48. Only a vertical translation is required to form a single motion.

  As shown in FIG. 3, the pair of side walls 52 at the outlet 46 is inclined at a similar or equal inclination angle B so as to extend outward from the common inlet 44. Correspondingly, the EDM electrode 54 is locally applied from its thin distal end within the jog region below the shank to correspondingly form the two sidewalls 52 in the common electrical discharge machining formation of the tip hole 42. It is spreading.

  The exemplary configuration of the tip hole shown in the two orthogonal planes of FIGS. 2 and 3 can be derived from a conventional axisymmetric diffusion hole common in turbine blade cooling. However, instead of being axially symmetric, the tip hole 42 shown in FIG. 3 is symmetric only in the chord direction along the squealer rib 34 between the leading edge and the trailing edge in order to spread the discharge cooling air. In order to deflect or deflect the discharged cooling air outwardly from the hole towards the adjacent inner surface of the squealer rib 34, the difference is that it is asymmetric or not symmetric in the blade thickness section shown in FIG.

  In a typical diffusion hole, the diffusion angle of the spreading wall is limited to a value that avoids flow separation of the discharge cooling air from the diffusion wall and maximizes the diffusion effect. Furthermore, the conventional diffusion angle remains the same as in a conventional axisymmetric diffusion hole.

  In the exemplary embodiment shown in FIGS. 2 and 3, the forward wall 48 of the tip hole is inclined toward the rib 34 with an acute angle of inclination A, preferably greater than the angle of inclination B of the outlet side wall 52. For example, the blade thickness direction inclination angle A can be about 27 ° and the chord direction inclination angle B can be about 22 ° to obtain an overall chord direction spread of about 44 °.

  In this way, the air discharged from the tip hole can spread in the chord direction along the length of the squealer rib 34 as shown in FIG. 3, and has a greater influence on the base of the squealer rib 34. Can be slanted or bent as given. Since the front wall 48 is inclined and the rear wall 50 is vertical, the air discharged from the tip hole will spread over the range of angles between them. The front wall 48 is preferably positioned proximate to the inner surface of the squealer rib 34, but to prevent the squealer rib itself from being subjected to stray discharge machining when drilling a hole, the required offset spacing shown in FIG. Limited by C.

  The larger inclination angle A of the front wall 48 causes the discharged cooling air to have a greater cooling effect closer to the proximal end of the squealer rib 34, and this large cooling effect thereafter causes the air to flow upward so that the Helps ensure that it can continue to a high position, such as passing through the distal end.

  The air that grazes the squealer ribs from the tip holes provides a type of impingement cooling that is otherwise perpendicular to the surface, as well as film cooling of the rib inner surface. Further, the excessive inclination angle A of the front wall 48 can cause discharge air flow separation and promote turbulence therein, which increases heat transfer and further cools the inner surface of the squealer rib. Improve.

  2-4 show that the squealer ribs 34 are integrally joined to the tip floor 28 with a relatively small fillet having a radius of about 5 to 20 mils (0.13 to 0.5 mm) and the tip hole outlet 46. Shows one embodiment that terminates at or close to the fillet 56. For example, in order to provide the tip hole 42 as close as possible to the inner surface of the squealer rib 34, the fillet 56 can be made as small as practical. Also, in order to ensure that the tip hole is located as close as possible to the squealer rib 34 without causing stray discharge machining of the squealer rib itself during drilling of the hole, the dimensions of the fillet 56 are as shown in FIG. Can be selected so as to coincide with the interval C shown in FIG.

  5 and 6 show another embodiment of the tip hole 42 in which the base of the squealer rib 34 and the fillet 56 at the tip floor 28 are relatively large and the outlet 46 of the tip hole 42 is Large enough to terminate at least partially or entirely within the fillet 56. FIG. 5 shows the radius R of the fillet 56 sufficient to completely encompass the outlet of the tip hole 42.

  In this way, the outlet of the tip hole increases from a rear wall 50 whose height is vertical to the inclined front wall 48, and the two side walls 52 gradually increase in height between them. The taller sidewall can then be used to further confine this cooling air when it is discharged from the outlet. In addition, the increased side walls also promote early cooling of the squealer ribs 34 closer to the base of the squealer ribs 34 that join the side walls at the large fillet 56.

  7-9 illustrate yet another embodiment of the angled tip hole 42, in which the tip cavity 36 is integral at the junction between the tip floor 28 and the base of the rib 34. It includes a plurality of lugs or bosses 58 that are joined or cast and spaced laterally or chordally along the ribs between the leading and trailing edges of the airfoil.

  Each lug 58 is then provided with a small flat area raised upward from the reference height of the tip floor within which the corresponding one of the tip holes 42 is in flow communication with the internal cooling circuit 24. Can extend radially through. In this way, all four walls 48, 50, 52 of the hole outlet 46 have their height extending radially outward at the base of the corresponding squealer rib 34 to increase internal convection cooling at the base of the rib. Further, the discharge air can be further restrained so as to be inclined toward the inner surface of the squealer rib while spreading in the lateral direction along the chord direction of the squealer rib.

  Since the lug is installed at the radially outer end of the airfoil and generates a centrifugal load during operation, the tip floor 28 can remain relatively thin and the lug 58 is provided only locally to accommodate The outlet 46 of the tip hole is bounded and the discharge of the cooling air from the outlet 46 is controlled.

  FIG. 8 schematically illustrates an exemplary method of fabricating a turbine blade, which includes a solid tip floor 28 and an adjacent squealer rib 34 and cast lugs integrally therewith. As a unitary structural component, it is first cast as usual. In this configuration, the outlet portion 46 of each tip hole 42 can be cast from the beginning into the corresponding lug 58 by virtue of their relatively large and widening dimensions. However, the small inlet 44 is too small for casting and the tip floor 28 remains solid in this area after the casting process.

  Thus, following the initial casting of the turbine blade, then any conventional method is used to drill the corresponding inlet 44 through the corresponding lug 58 and tip floor 28 in flow communication with the internal cooling circuit 24. Can be processed. Since the outlet 46 is pre-cast, the inlet 44 can be drilled straight through the lug vertically without the need for an offset EDM electrode as shown in FIG. The drilling of the inlet 44 can be accomplished using, for example, conventional laser drilling or EDM drilling with a simple linear electrode with small dimensions to match the intended dimensions of the inlet 44.

  A particular advantage of pre-casting the lug 58 is that the widened and curved outlet 46 can be additionally cast in any desired configuration. For example, the outlet rear wall 50 shown in FIGS. 8 and 9 can now be inclined outwardly from the inlet 44 toward the skier rib 34 and also toward the inclined front wall 48. The rear wall 50 slopes in the same direction as the front wall 48, but can have a smaller acute slope to widen the outlet 46 between the inlet and the squealer rib.

  In this embodiment, the tip hole inlet 44 extends perpendicularly or substantially at right angles to the tip floor 28 and the rear wall 50 is slightly inclined so that the inlet is partially as shown in FIG. It extends through the central part of the rear wall 50 and forms a local notch there by drilling. However, the remaining portion of the rear wall 50 forms a slight overhang above the inlet 44 below it, helping to skew the discharge air flow so that the squealer ribs 34 are grazed.

  In the various embodiments disclosed above, the inlet 44 will meter the discharge air to a predetermined amount relative to the airfoil. The inlet 44 can have any suitable shape, from rectangular to circular and oval, as desired and manufactured in an economical manner.

  The slanted outlet is asymmetric in the blade thickness direction towards the squealer ribs to be cooled, thus allowing all of the inlet air to be directed outwards towards the ribs and towards the center of the tip cavity. Minimize any loss, if any. The advantage of using a widening configuration at the hole outlet can be obtained by diffusing the discharged cooling air and further bending or deflecting the cooling air directly towards the skier rib to enhance cooling of the skier rib.

  While this specification has described what is considered to be preferred and exemplary embodiments of the invention, other modifications of the invention will become apparent to those skilled in the art from the teachings herein. Therefore, we hope that all such modifications will be protected by the following claims as falling within the spirit and scope of the invention.

  Accordingly, what is desired to be secured by Letters Patent application is the invention as defined and identified by the following claims.

1 is a perspective view of a portion of an exemplary gas turbine engine first stage rotor blade extending radially outward from an outer periphery of a support rotor disk. FIG. Front sectional drawing of the front-end | tip part of the airfoil part shown in FIG. 1 taken along line 2-2. FIG. 2 is an axial side cross-sectional view of the airfoil tip shown in FIG. 1 taken along line 2-2. FIG. 4 is a top view of the tip of the airfoil shown in FIG. 3 taken along line 4-4. The front sectional view similar to FIG. 2 of the airfoil tip according to another embodiment. FIG. 6 is a top view of a portion of the airfoil tip shown in FIG. 5 taken along line 6-6. FIG. 2 is a cross-sectional perspective view of the tip portion of the airfoil shown in FIG. 1 according to another embodiment, taken generally along line 2-2. FIG. 8 is an enlarged front cross-sectional view of a portion of the tip of the airfoil shown in FIG. 7 according to the manufacturing method of the present invention. FIG. 9 is a top view of a portion of the airfoil tip shown in FIG. 8 taken along line 9-9.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 Turbine blade 12 Airfoil part 14 Platform 16 Dovetail 18 Rotor disk 20 Pressure side wall 22 Negative pressure side wall 24 Cooling circuit 26 Root 28 Tip floor 30 Leading edge 32 Trailing edge 34 Skittle rib 36 Tip cavity 38 Cooling air 40 Combustion gas 42 Tip hole 44 Inlet 46 Outlet 48 Front wall 50 Rear wall 52 Side wall 54 (EDM) electrode 56 Fillet 58 Lug

Claims (10)

An airfoil (12) formed integrally with the support dovetail (16) and extending outwardly from the platform (14) at the root (26);
The airfoil (12) includes opposing positive and negative pressure sidewalls (20, 22) spaced apart and forming an internal cooling circuit (24) therein, from the root (26) Extends across the wing length to the tip floor (28) at the opposite distal end and extends across the chord between the opposite leading and trailing edges (30, 32);
Skira ribs (34) extend from the side walls (20, 22) around the floor (28) to form an open tip cavity (36) on the floor;
A plurality of curved tip holes (42) extend through the floor in flow communication with the cooling circuit (24) to receive cooling air (38) from the cooling circuit (24), and cooling air (38 ) At an angle toward the rib so as to orient the squealer rib (34).
Turbine rotor blade (10).   Each of the tip holes (42) passes through a bottom surface of the floor (28) and extends almost vertically, and a slanted outlet (46) curved from the inlet toward the rib (34). The blade according to claim 1.   The blade according to claim 2, wherein the outlet (46) has a flow passage area that widens from the inlet (44) so as to diffuse cooling air (38) discharged from the outlet. Said outlet (46)
A flat front wall (48) inclined outwardly from the inlet (44) toward the rib (34);
A flat rear wall (50) spaced inwardly from the front wall (48);
A pair of flat side walls (52) that join the front and rear walls (48, 50) together to surround the outlet (46);
The blade of claim 3, comprising:   The blade of claim 4, wherein the rib (34) joins the floor (28) at a fillet (56) and the outlet (46) terminates at the fillet (56).   The blade of claim 5, wherein the rear wall (50) is collinear with the inlet (44).   The blade according to claim 5, wherein the rear wall (50) is inclined outwardly from the inlet (44) towards the inclined front wall (48).   The blade according to claim 5, wherein the pair of side walls (52) of the outlet (46) is inclined to expand outwardly from the inlet (44).   The blade according to claim 8, wherein the front wall (48) is inclined towards the rib (34) with an inclination angle greater than the inclination of the outlet side wall (52). A plurality of lugs (58) integrally joined to the floor (28) and ribs (34) and spaced along the ribs;
Each of the lugs (58) includes a corresponding one of the tip holes (42) extending through the lugs in flow communication with the cooling circuit (24).
The blade according to claim 5.

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